efi: Don't use knowledge about efi_guid_t internals

When print GUIDs supply pointer to the efi_guid_t (guid_t) type rather
its internal members.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>